Keeping Time with the Skies
NoteWhat This Chapter Covers
Long before clocks and calendars, people read time in the sky. This chapter explains why the Moon changes shape through its phases (and why that has nothing to do with Earth’s shadow), then shows how three sky cycles gave us our units of time: the Sun’s daily march → the day, the Moon’s phases → the month, and the Earth’s journey around the Sun → the year. From these come lunar, solar and luni-solar calendars — including the Indian National Calendar — which set the dates of our festivals. We finish with the newest objects in the sky: artificial satellites and India’s space missions.
Learning Outcomes
By the end of this chapter, you will be able to:
- name the phases of the Moon and explain that they arise from the changing Sun–Moon–Earth positions (not Earth’s shadow);
- explain how the day, month and year come from the rotation of the Earth, the Moon’s phases, and the Earth’s revolution;
- distinguish lunar, solar and luni-solar calendars, and explain the leap year;
- connect Indian festivals to the Moon’s phases and calendars;
- describe artificial satellites, their uses, and major ISRO missions.